A new Ni(II) complexes based on L-amino acids derived ligands: synthesis, characterization and study of the role of the supramolecular structure in the carbon dioxide capture

O.C. SANCHEZ MONTILVA; A. RIVAS MARQUINA; F. DI SALVO; F. MOVILLA

San Carlos de Bariloche

Congreso; XY Reunion Anual de laAACr; 2019

Amino acid derivatives can be considered as excellent candidates to act as ligands in the synthesis of coordination compounds due to the presence of the carboxylate and amino groups. Furthermore, the relative position of both functionalities makes them suitable as chelates.[1] Other advantage of metal coordination compounds based on amino acids ligands is related to their use as catalysts because they can be capable of transmitting chiral information during the stereoselective process.[2] Based on these features, we synthesized a new family of chiral compounds obtained from the N-derivatization reaction of L-α-amino acids with the aldehyde piperonal and a subsequent reduction. Then, the reaction of the L-tyrosine (1) and L-phenylalanine (2) derivatives with Ni(II) salts gave place to coloured solids which were assigned as the corresponding coordination compounds. For both molecules and with all the studied salts, the conditions chosen for the synthesis after a careful optimization, were two equivalents of the ligand as sodium salt, and one of the metal ion using methanol as solvent. The results obtained for ligand 1 and different Ni(II) salts (acetate, nitrate, chloride and sulphate), were very similar; in all cases large green-blue single crystals (1Ni-SC). The structure was confirmed by single crystal X-ray diffraction (XRD) experiments performed on 1Ni-SC crystals and for all Ni(II) salts it was observed a trinuclear complex with a carbonate as bridging ligand of three metal ions. The carbonate anion is derived from the CO2 present in the atmosphere and once it is spontaneously absorbed by the reaction mixture, it self-assembles into the trinuclear system. A similar synthetic procedure was followed for ligand 2, but in all cases instead of single crystals, light blue sphere-like crystalline aggregates constructed by nano and micro crystals (2Ni-CA) were obtained. Using other crystallization conditions single crystals (2Ni-SC) were obtained and XRD results showed a mononuclear octahedral Ni(II) complex bearing two molecules of 2 as chelating ligands and two water molecules occupying the remaining sites. The structural results obtained by single crystal XRD studies proved that the key factor to sustain the supramolecular structure responsible for the CO2 uptake in the L-Tyrosine derivative complex, is the OH group of the amino acid bone, which is absent in the L-Phenylalanine analogue.